Method of sharpening worn-out files.



UNITED STATES PATENT OFFIGE.

FRANK ROWLEY, OF WHALEY BRIDGE, ENGLAND.

METHOD OF SHARPENING WQRN-OUT FILES.

SPECIFICATION forming part of Letters Patent No. 685,299, dated October29, 1901.

Application filed March 16, 1901. Serial No. 51,464. (No specimens.)

To all whom it may concern.-

Be it known that I, FRANK ROWLEY, a sub get of the Queen of GreatBritain, residing at ock Cottage, Whaley Bridge, in the county ofChester, England, have invented new and useful Improvements in theProcess of Sharpening Worn-Out Files, of which the following is aspecificationt This invention relates to the method of sharpening filesdescribed in the British patent specification, No. 19,326, A. D. 1893;and it consists in the hereinafter-described improvements therein. Incarrying out the said method it has been found that notwithstand- I 5ing a thorough cleansing of the files in soap and soda and rinsing inwater the nitric acid in many cases was acting slowly and irregularly inattacking and biting away the bottom and sides of the teeth.

The object of my improvement is to render the action of the nitric acidmore certain and regular. For this purpose after washing and brushingthe files with soap and soda and rinsing them in water I immerse andpickle them for about half an hour in diluted sulfuric acid, one part ofcommercial acid being mixed with about four parts of water. The sulfuricacid slightly corrodes or attacks the surface of the file and preparesit for the subsequent action of the nitric acid, imparting a surface tothe file which enables the subsequent process to operate more certainlyand efficiently and to produce a greater and more uniform sharpness ofthe tooth than when such pre* 5 liminary pickling is not applied Withthe same object after pickling the files in sulfuric acid, as aforesaid,I also draw the point of a needle through all the grooves of the file,slightly scraping or scratching the surface of the bottom of thegrooves, in consequence of which the nitric acid is enabled to act morecertainly at this point and bite away the sides of the teeth from thebottom toward the top. After cleaning and drying the files I coat theworn or fiat tops of the teeth with varnish, such as Brunswick black,capable of resisting the corrosive action of acids, and immerse them ina mixture of nitric acid and water in the manner described in theaforesaid specification till the bottom and sides of the teeth arebitten away sufficiently to throw off the fiat tops, leaving thenewly-formed teeth Very sharp.

I claim as my invention- The method of sharpening worn-out files by 5 5first cleansing them with soap and soda and rinsing them in water, thenimmersing them in diluted sulfuric acid and drawing a needie-pointthrough the grooves of the file, cleaning and drying them, coating theworn -6o tops with 'a varnish capable of resisting the corrosive actionof acids and immersing them in diluted nitric acid.

In testimony whereof I have hereunto set my hand in the presence of twowitnesses FRANK ROWLEY.

Witnesses:

R. J. URQUHART, O. BoLLn.

